Behavioural and eco-physiological responses of the mussel Mytilus galloprovincialis to acidification and distinct feeding regimes

Abstract

The carbon dioxide taken up by the ocean is increasing as levels of atmospheric carbon dioxide increase, thus lowering the ocean pH and altering the carbonate system. In this laboratory study, we evaluated the physiological responses of juvenile mussels (Mytilus galloprovincialis) from Galician waters (NW Iberian Peninsula) exposed to control (500 µatm) and elevated (800 or 1200 µatm) seawater pCO2 conditions under two different feeding regimes (optimal and suboptimal). Shell properties such as compressive strength and composition (organic matter and aragonite-calcite ratio) were negatively affected by high seawater pCO2, regardless of food availability. This result indicated water chemistry as a main driver for shell development. Under the optimal feeding regime, mussel feeding rates increased in response to elevated pCO2, presumably as a strategy to maintain a high strength of attachment. By contrast, mussels under the suboptimal diet showed weak 2 attachment and narrow valve opening at the highest pCO2 condition. In conclusion, under optimal food availability, mussels were resilient to water acidification when considering metrics such as feeding activity, valve opening and attachment strength. Under a suboptimal diet, however, the ability of mussels to respond to acidification was compromised. These results highlight complex ecophysiological interactions for calcifying organisms subjected to climate change.

The Mediterranean mussel Mytilus galloprovincialis: responses to climate change scenarios as a function of the original habitat

“…Any strategy that can cope with decreased seawater pH or any other stress factor will be energetically demanding. The energetic costs of both biomineralization and byssogenesis processes are consistent with relatively higher maintenance ranges, and extra stressors such as food scarcity may further exacerbate the negative impact of OA ( Melzner et al , 2011 ; Mackenzie et al , 2014 ; Lassoued et al , 2019 ).…”

“…The pH was measured by the spectrophotometric method described by Clayton and Byrne (1993 ). More detailed information about the analytical methods is provided in a previous article ( Lassoued et al , 2019 ). Calculations were carried out using the equations proposed by Dickson et al (2007 ), who included a correction factor for the difference between seawater and the acidity indicator.…”

“…The system was constructed by glueing (with cyanoacrylate glue) a coated Hall element sensor to a valve and then glueing a magnet (4.8-mm diameter × 0.8-mm height) to the other valve, on exactly the opposite side of the Hall sensor. For other specifications of this technique, see Comeau et al (2018) and Lassoued et al (2019) for similar experimental set-up. Valve opening was monitored at an interval of one measurement per second throughout the whole experimental period.…”

“…This effect is derived from the fact that shell (growth) maintenance may compromise shell functioning through energetically costly metabolic compensation for the increased shell dissolution that occurs under OA ( Mackenzie et al , 2014 ). Nevertheless, neutral or even positive effects of OA have also been described regarding specific metabolic responses ( Ries et al , 2009 ; Melzner et al , 2011 ; Fernández-Reiriz et al , 2012 ; Range et al , 2012 ; Gazeau et al , 2014 ; Mackenzie et al , 2014 ), especially when food resources are optimal during the maintenance of individuals through increasing feeding activity ( Lassoued et al , 2019 ). These very variable responses may be explained by the distinct pH-regulation values considering species-specific capacities ( Fabry et al , 2008 ) and also different life-history stages of the same species, e.g.…”

Animal size and sea water temperature, but not pH, influence a repeatable startle response behaviour in a wide-ranging marine mollusc

“…Clumping behaviour in Mytilus edulis (Kong et al, 2019) was affected by acidification; however multiple studies suggest no effect on baseline valve gaping activity in marine bivalves, even under extremely low pH conditions (pH < 7) (Bamber & Westerlund, 2016;Clements et al, 2018;Jakubowska & Normant, 2015). Furthermore, while valve gaping in Mytilus galloprovincialis was affected by acidification when food was reduced, normal feeding regimes saw no effect (Lassoued et al, 2019). While it could be argued that the lack of pH effect is due to the cue type used (i.e., tactile versus olfactory), a recent study on Mytilus galloprovincialis found no effect of low pH on valve closure responses to chemical alarm cues ..…”